This invention relates to apparatus for measuring the electrolyte temperature in a storage battery and more particularly relates to such apparatus particularly useful where physical access to the battery electrolyte is either not possible or not convenient without destruction of all or a portion of the battery and further contemplates the provision of automatic battery analyzing apparatus including such temperature measuring apparatus.
There has in the past been much effort at developing apparatus for determining the condition of storage batteries such as the lead-acid type normally used for starting, lighting, and ignition in the automotive field and, in particular, for determining the acceptability of such batteries for use under adverse conditions such as the starting of an automobile engine at low temperatures. It has been known in the past that in making such a determination the temperature of the battery at the time any tests are being made thereon must be taken into account since the performance of a lead-acid storage battery varies widely with variations in temperature. The advent of automotive batteries with either no means for access to the battery electrolyte or with such means suitable for only infrequent use has created a need for apparatus for determining the acceptability of a battery which apparatus does not require any access to the interior of the battery or any physical contact with the battery electrolyte and which is also capable of compensating for the temperature of the battery under test. The testing of automotive batteries is further complicated by the conditions under which they are commonly tested. Since the performance of automotive batteries is most critical during cold weather, such batteries are most often tested during cold weather when, for example, the battery itself may be at a very low temperature, often many degrees below freezing, because it has been outside for a prolonged period of time. However, the actual testing of the battery may be performed in a relatively warm environment when a battery already in service is removed from the automobile and taken inside for testing or the automobile is driven into a service bay. In such instances, the battery electrolyte normally will be at approximately the ambient outside temperature, but the portions of the battery conveniently accessable for measuring temperature, such as the battery connector or post, will not be at the battery electrolyte temperature but rather at some temperatures intermediate the electrolyte temperature and the ambient inside temperature. It is important that the battery temperature be determined sufficiently accurately that the results of the battery test are not adversely effected; it is particularly important that the temperature be determined accurately in the low temperature range because of the relative ineffeciency of battery operation at low temperatures and the sensitivity of battery efficiency to relatively small temperature changes.
Apparatus for automatically analyzing the condition of an automotive battery including circuitry attempting to account for the battery temperature are known in the prior art. Such apparatus and various of the desideratum of such apparatus are disclosed in the U.S. patent application of C. E. Frailing and T. J. Dougherty, Ser. No. 863,925, filed Dec. 23, 1977 now Pat. No. 4,193,025, entitled "Automotive Battery Analyzer" and assigned to the assignee of this application, now U.S. Pat. No. 4,193,025 which issued on Mar. 11, 1980. The disclosure of that application is hereby incorporated by reference. The apparatus shown therein took temperature measurements of the battery's negative terminal or post at two times, the time at which the leads of the apparatus were connected to the battery terminals and the time five seconds later. On the basis of empirical observation, it was estimated that the difference between the two measured temperatures was approximately one-fourth of the difference between the initial measured temperature and the actual battery temperature, and this approximation was used to calculate an estimated battery temperature. However, further work with automatic battery analyzers has shown that increased accuracy over that provided by the prior approach is desirable.
In the design of temperature measuring apparatus for use with automotive battery analyzers, a number of criteria must also be considered in addition to the accuracy of the resultant measurement. It is necessary that the apparatus not be so complex that relatively unskilled personnel would have difficulty in using it. It is desirable that the apparatus be useful with a wide variety of different types of battery designs. Specifically, it is desirable that the apparatus be useful with batteries of the traditional type having the connector posts located on the top surface of the battery as well as with batteries of the more recently introduced type having posts located on a side surface of the battery. It is necessary that the apparatus be useful when the battery is either in an automobile in its normal service location or removed from the automobile. It is also desirable that the apparatus be of such a physical construction that it can be used in a wide variety of automobiles which, for example, may have battery covers, battery shields or cases, structural members of the automobile, or other components of the automobile located in different physical relationships to, and closely adjacent, the battery. Finally, it is necessary that the temperature measuring apparatus not be such that either the temperature measurement itself or the period required for the associated battery analyzer circuit to test a battery be undersirably long.